Long-Term Debt (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($) number_of_interest_rate_swaps	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Total	$ 11,922.5	$ 10,387.6
Integrys acquisition fair value adjustment	14.3	20.6
Unamortized debt issuance costs	(52.9)	(44.7)
Unamortized discount, net and other	(25.6)	(27.8)
Long-term debt, including current portion	11,858.3	10,335.7
Current portion of long-term debt	(686.9)	(360.1)
Total long-term debt	11,171.4	9,975.6
Finance lease obligation	45.9	23.3
Future maturities of long-term debt outstanding
2020	686.9
2021	1,338.8
2022	390.8
2023	42.8
2024	570.0
Thereafter	8,893.2
Total	$ 11,922.5	$ 10,387.6
WE
Debt Instrument [Line Items]
Weighted Average Interest Rate	4.26%	4.50%
Unsecured debt	$ 2,785.0	$ 2,735.0
WE \| WE Debentures (unsecured), 2.05% due 2024
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	2.05%
Proceeds from issuance of debt	$ 300.0
WE \| WE Debentures (unsecured), 4.25% due 2019
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	4.25%
Repayments of Unsecured Debt	$ 250.0
WPS
Debt Instrument [Line Items]
Weighted Average Interest Rate	4.04%	4.21%
Senior notes	$ 1,625.0	$ 1,325.0
WPS \| WPS Senior Notes (unsecured), 3.30% due 2049
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	3.30%
Proceeds from issuance of debt	$ 300.0
WG
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.65%	4.04%
Unsecured debt	$ 640.0	$ 490.0
WG \| WG Debentures (unsecured), 2.38% due 2024
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	2.38%
Proceeds from issuance of debt	$ 150.0
Integrys Holding Inc
Debt Instrument [Line Items]
Weighted Average Interest Rate	4.17%	4.17%
Senior notes	$ 250.0	$ 250.0
Integrys Holding Inc \| Integrys Junior Notes (unsecured), 6.00% due 2073
Debt Instrument [Line Items]
Weighted Average Interest Rate	6.00%	6.00%
Unsecured debt	$ 400.0	$ 400.0
Debt instrument interest rate stated percentage rate	6.00%
Debt Instrument, Basis Spread on Variable Rate	3.22%
PGL
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.59%	3.88%
Secured debt	$ 1,520.0	$ 1,195.0
PGL \| PGL Series WW Bonds (secured), 1.875% due 2033
Debt Instrument [Line Items]
Secured debt	$ 50.0
Debt instrument interest rate stated percentage rate	1.875%
PGL \| PGL Series GGG (secured), 2.96% due 2029
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	2.96%
Proceeds from issuance of debt	$ 275.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 4.63% due 2019
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	4.63%
Repayments of Secured Debt	$ 75.0
PGL \| PGL Series HHH (secured), 2.64% due 2024
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	2.64%
Proceeds from issuance of debt	$ 75.0
PGL \| PGL Series III (secured), 3.06% due 2031
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	3.06%
Proceeds from issuance of debt	$ 50.0
NSG
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.81%	3.81%
Secured debt	$ 132.0	$ 132.0
MERC
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.51%	3.51%
Senior notes	$ 120.0	$ 120.0
MGU
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.51%	3.51%
Senior notes	$ 90.0	$ 90.0
UMERC
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.26%
Senior notes	$ 160.0	$ 0.0
UMERC \| UMERC Senior Notes (unsecured), 3.26% due 2029
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	3.26%
Proceeds from issuance of debt	$ 160.0
Bluewater Gas Storage, LLC
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.76%	3.76%
Senior notes	$ 120.3	$ 122.7
ATC Holding LLC
Debt Instrument [Line Items]
Weighted Average Interest Rate	4.05%	4.34%
Senior notes	$ 475.0	$ 240.0
ATC Holding LLC \| ATC Holding Senior Notes (unsecured), 3.75% due 2029
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	3.75%
Proceeds from issuance of debt	$ 235.0
We Power
Debt Instrument [Line Items]
Weighted Average Interest Rate	5.57%	5.56%
Secured debt	$ 1,005.2	$ 1,037.9
WECC
Debt Instrument [Line Items]
Weighted Average Interest Rate	6.94%	6.94%
Unsecured debt	$ 50.0	$ 50.0
WEC Energy Group
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.47%	3.54%
Senior notes	$ 2,050.0	$ 1,700.0
Current portion of long-term debt	(400.0)	0.0
Total long-term debt	2,141.6	$ 2,190.8
Future maturities of long-term debt outstanding
2020	400.0
2021	600.0
2022	350.0
2023	0.0
2024	0.0
Thereafter	$ 1,200.0
WEC Energy Group \| WEC Energy Group senior notes (unsecured), 6.20% due 2033
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	6.20%
WEC Energy Group \| WEC Energy Group Junior Notes (unsecured), 3.53% due 2067
Debt Instrument [Line Items]
Weighted Average Interest Rate	4.50%	4.85%
Unsecured debt	$ 500.0	$ 500.0
Debt instrument interest rate stated percentage rate	4.02%	4.73%
WEC Energy Group \| WEC Senior Notes (unsecured), 3.10% due 2022
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage rate	3.10%
Proceeds from issuance of debt	$ 350.0
WEC Energy Group \| Interest rate swaps
Debt Instrument [Line Items]
Number of interest rate swaps executed \| number_of_interest_rate_swaps	2
Interest rate swap fixed interest rate	4.9765%
Interest rate swap notional value	$ 250.0

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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